In electrophotography, also known as Xerography, electrophotographic imaging or electrostatographic imaging, the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light. The radiation selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image on the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as transparency or paper. The imaging process may be repeated many times with reusable imaging members.
Although excellent toner images may be obtained with multilayered belt or drum photoreceptors, it has been found that as more advanced, higher speed electrophotographic copiers, duplicators, and printers are developed, there is a greater demand on print quality. The delicate balance in charging image and bias potentials, and characteristics of the toner and/or developer, must be maintained. This places additional constraints on the quality of photoreceptor manufacturing, and thus on the manufacturing yield.
Imaging members are generally exposed to repetitive electrophotographic cycling, which subjects the exposed charged transport layer or alternative top layer thereof to mechanical abrasion, chemical attack and heat. This repetitive cycling leads to gradual deterioration in the mechanical and electrical characteristics of the exposed charge transport layer. Physical and mechanical damage during prolonged use, especially the formation of surface scratch defects, is among the chief reasons for the failure of belt photoreceptors. Therefore, it is desirable to improve the mechanical robustness of photoreceptors, and particularly, to increase their scratch resistance, thereby prolonging their service life.
Providing a protective overcoat layer is a conventional means of extending the useful life of photoreceptors. Conventionally, for example, a polymeric anti-scratch and crack overcoat layer has been utilized as a robust overcoat design for extending the lifespan of photoreceptors. The conventional formulation comprises a (i) an acrylic or polyester polyol binder, (ii) an optional melamine-formaldehyde curing agent, (iii) a tertiary aromatic amine hole transport material; (iv) an acid catalyst, and (v) a leveling agent coated from a solution using one or more alcohol solvents such as dowanol and/or isopropanol. In conventional formulations, Silclean 5705 leveling agent, commercially available from BYK Chemicals, is sometimes added with the objective of improving the coating properties of the solution and/or coating quality of the final protective overcoat layer.
However, the conventional overcoat layer formulation exhibits unacceptably low scratch resistance, low coating quality and results in a comparatively rough surface, which can make cleaning the toner difficult.
Despite the various approaches that have been taken for forming imaging members there remains a need for improved imaging member design, to provide improved imaging performance and longer lifetime, reduce human and environmental health risks, and the like.